The disclosure relates to heating ventilation and air conditioning (HVAC) systems. More particularly, the disclosure relates to small capacity systems such as residential air conditioning (AC) or heat pump systems.
A common configuration of small capacity residential HVAC system is a split single loop system wherein an outdoor unit includes the compressor and an outdoor heat exchanger (heat rejection heat exchanger in a cooling/air conditioning mode) and an associated fan. An indoor unit includes an indoor heat exchanger (heat absorption heat exchanger or evaporator in the cooling/air conditioning mode) and associated fan. The indoor unit may be associated with ducts for delivering air throughout the building. An exemplary compressor is a rotary or scroll compressor which may be synchronously electrically driven. An exemplary refrigerant is R410A.
In the cooling/AC mode, refrigerant cooled in the outdoor heat exchanger is passed via a refrigerant line to the evaporator. An expansion device may be located in the indoor unit to further reduce refrigerant temperature prior to its passing through the indoor heat exchanger. Warmed refrigerant vapor is then passed from the indoor unit back to the compressor.
For more than a decade, efforts have been made to develop systems using low global warming potential (GWP) refrigerants. One example of a low-GWP refrigerant is R1233zd(E) (hereafter simply “R1233zd”). Whereas, R410A has a direct GWP of 2088, R1233zd has a direct GWP of less than 1.0. R1233zd also has a higher cycle efficiency than R410A (e.g., by about 10% to 15%) due to lower discharge temperatures and lower expansion losses. Nevertheless, R1233zd suffers from being a low pressure refrigerant. A low pressure refrigerant is defined by the United States Environmental Protection Agency (EPA) as having a saturation pressure less than 45 psia (310 kPa) (R1233zd has a saturation pressure of 31 psia (214 kPa)) at 104° F. (40° C.). Low pressure refrigeration systems typically operate at evaporator pressures (thus compressor suction pressures) less than atmospheric pressure or the ambient pressure which might slightly differ from 1 ATM due to weather, altitude, etc.
R410A (saturation pressure 352 psia (2.43 MPa) at 104° F.) is a high-pressure refrigerant (saturation pressure 170 psia (1.17 MPa) to 355 psia (2.45 MPa) at 104 F). R134a (saturation pressure 147 psia (1.01 MPa) at 104° F.) is a medium pressure refrigerant (saturation pressure 45 psia (310 kPa) to 170 psia (1.17 MPa) at 104° F.).
R1233zd also has benefits of being non-flammable and nontoxic (rating A1 under ASHRAE Standard 34-2007; with “A” indicating non-toxic and “1” indicating non-flammability).
As a practical matter, R1233zd applicability has been limited to large capacity systems which tend to be less sensitive to size and packaging problems and tend to be less sensitive to up-front hardware costs.